The inventions described herein generally relate to semiconductor devices and a fabrication processes thereof. More particularly, the inventions relate to a forming an insulation film and fabrication process of a non-volatile semiconductor memory device capable of rewriting information electrically, including a flash memory device.
There are various volatile memory devices such as DRAMs and SRAMs. Further, there are non-volatile memory devices such as a mask ROM, PROM, EPROM, EEPROM, and the like. Particularly, a flash memory device is an EEPROM having a single transistor for one memory cell and has an advantageous feature of small cell size, large storage capacity and low power consumption. Thus, intensive efforts are being made on the improvement of flash memory devices. In order that a flash memory device can be used stably over a long interval of time with low voltage, it is essential to use a uniform insulation film having high film quality.
Further, high-quality insulation film, characterized by uniform film quality and low leakage current, is important not only in a flash memory device but also in other various semiconductor devices that uses a capacitor, including a ferroelectric semiconductor memory device that uses a ferroelectric film. Further, a high dielectric film of uniform film quality characterized by small leakage current is important as a gate insulation film of a high-speed semiconductor device having a gate length of 0.1 xcexcm or less.
First, the construction of a conventional flash memory device will be explained with reference to FIG. 1 showing the concept of a generally used flash memory device having a so-called stacked gate structure.
Referring to FIG. 1, the flash memory device is constructed on a silicon substrate 1700 and includes a source region 1701 and a drain region 1702 formed in the silicon substrate 1700, a tunneling gate oxide film 1703 formed on the silicon substrate 1700 between the source region 1701 and the drain region 1702, and a floating gate 1704 formed on the tunneling gate oxide film 1703, wherein there is formed a consecutive stacking of a silicon oxide film 1705, a silicon nitride film 1706 and a silicon oxide film 1707 on the floating gate 1704, and a control gate 1708 is formed further on the silicon oxide film 1707. Thus, the flash memory of such a stacked structure includes a stacked structure in which the floating gate 1704 and the control gate 1708 sandwich an insulating structure formed of the insulation films 1705, 1706 and 1707 therebetween.
The insulating structure provided between the floating gate 1704 and the control gate 1705 is generally formed to have a so-called ONO structure in which the nitride film 1706 is sandwiched by the oxide films 1705 and 1707 for suppressing the leakage current between the floating gate 1704 and the control gate 1705. In an ordinary flash memory device, the tunneling gate oxide film 1703 and the silicon oxide film 1705 are formed by a thermal oxidation process, while the silicon nitride film 1706 and the silicon oxide film 1707 are formed by a CVD process. The silicon oxide film 1705 may be formed by a CVD process. The tunneling gate oxide film 1703 has a thickness of about 8 nm, while the insulation films 1705, 1706 and 1707 are formed to have a total thickness of about 15 nm in terms of oxide equivalent thickness. Further, a low-voltage transistor having a gate oxide film of 3-7 nm in thickness and a high-voltage transistor having a gate oxide film of 15-30 nm in thickness are formed on the same silicon in addition to the foregoing memory cell.
In the flash memory cell having such a stacked structure, a voltage of about 5-7V is applied for example to the drain 1702 when writing information together with a high voltage larger than 12V applied to the control gate 1708. By doing so, the channel hot electrons formed in the vicinity of the drain region 1702 are accumulated in the floating gate via the tunneling insulation film 1703. When erasing the electrons thus accumulated, the drain region 1702 is made floating and the control gate 1708 is grounded. Further, a high voltage larger than 12 V is applied to the source region 1701 for pulling out the electrons accumulated in the floating gate 1704 to the source region 1701.
Such a conventional flash memory device, on the other hand, requires a high voltage at the time of writing or erasing of information, while the use of such a high voltage tends to cause a large substrate current. The large substrate current, in turn, causes the problem of deterioration of the tunneling insulation film and hence the degradation of device performance. Further, the use of such a high voltage limits the number of times rewriting of information can be made in a flash memory device and also causes the problem of erroneous erasing.
The reason a high voltage has been needed in conventional flash memory devices is that the ONO film, formed of the insulation films 1705, 1706 and 1707, has a large thickness.
In the conventional art of film formation, there has been a problem, when a high-temperature process such as thermal oxidation process is used in the process of forming an oxide film such as the insulation film 1705 on the floating gate 1704, in that the quality of the interface between the polysilicon gate 1704 and the oxide film tends to become poor due to the thermal budget effect, etc. In order to avoid this problem, one may use a low temperature process such as CVD process for forming the oxide film. However, it has been difficult to form a high-quality oxide film according to such a low-temperature process. Because of this reason, conventional flash memory devices had to use a large thickness for the insulation films 1705, 1706 and 1707 so as to suppress the leakage current.
However, the use of large thickness for the insulation films 1705, 1706 and 1707 in these conventional flash memory devices has caused the problem in that it is necessary to use a large writing voltage and also a large erasing voltage. As a result of using large writing voltage and large erasing voltage, it has been necessary to form the tunneling gate insulation film 1703 with large thickness so as to endure the large voltage used.
Thus, there is a need of a high-quality insulation film that provides small leakage current even in the case the insulation film has a small thickness, wherein the need of such a high-quality insulation film is not limited to flash memory devices but also in other various semiconductor devices.
In general the inventions provide novel and useful arrangements and methods of forming a dielectric film wherein the foregoing problems are eliminated.
More specifically, the inventions provide a method of forming a high-quality oxide film, nitride film or oxynitride film in which reduction of film thickness is possible without causing substantial leakage current.
Also, the inventions provide a method of forming an oxide film characterized by the steps of:
forming an oxide film on a substrate; and
modifying a film quality of said oxide film formed on said substrate by exposing said oxide film to atomic state oxygen O*.
According to the inventions, the atomic state oxygen O* penetrate easily into the oxide film formed on the substrate and terminate dangling bonds or weak bonds in the oxide film. As a result, an SiO2 film formed by a process such as a CVD process can have a quality similar to that of a thermal oxide film as a result of exposure to the atomic state oxygen O*. Thus, the oxide film formed according to the present invention has various advantageous features such as small number of surface states, having a composition substantially identical with a stoichiometric composition, small leakage current, and the like. It should be noted that the atomic state oxygen O* can be formed efficiently by microwave excitation of a mixed gas of Kr and oxygen.
The inventions also provide a method of forming a nitride film that enables improvement of existing nitride film quality.
The inventions also provide a method of forming a nitride film, including:
forming a nitride film on a substrate; and
modifying a film quality of said nitride film formed on said substrate by exposing hydrogen nitride radicals NH*.
Hydrogen nitride radicals NH* penetrate easily into the nitride film formed on the substrate and compensates for defects in the nitride film. As a result, the nitride film has a near-stoichiometric composition of Si3N4 after the processing, and is characterized by small number of surface states and small leakage current. Further, there occurs relaxation of stress in the silicon nitride film thus processed. It should be noted that the hydrogen nitride radicals NH* are formed efficiently by microwave excitation of a mixed gas of Kr and oxygen.
The inventions also provide methods of forming an oxide film on a substrate by depositing the oxide film on the substrate by a CVD process, while simultaneously processing the deposited oxide film by atomic state oxygen formed in plasma.
The inventions also provide a method of forming an oxide film, including:
forming plasma in a processing chamber by introducing an inert gas of Kr or Ar and an oxygen gas into said processing chamber and causing microwave excitation therein;
causing a deposition of an oxide film on a substrate in said processing chamber by introducing a processing gas into said processing chamber and by causing activation of said processing gas by said plasma,
said oxide film being processed by atomic state oxygen O* formed in said plasma simultaneously to deposition.
The inventions also provide a method of forming a nitride film on a substrate by depositing the nitride film on the substrate by a CVD process, while simultaneously processing the nitride film thus deposited by hydrogen nitride radicals formed in plasma.
The inventions also provide a method of forming a nitride film including:
forming plasma in a processing chamber by introducing thereto an inert gas of Kr or Ar and a gas containing nitrogen and hydrogen and causing microwave excitation therein; and
depositing a nitride film on a substrate in said processing chamber by introducing a processing gas into said processing chamber and by causing activation of said processing gas by said plasma,
said silicon nitride film being processed by hydrogen nitride radicals NH* in said plasma simultaneously to deposition.
The inventions also provide a method of forming an oxynitride film on a substrate by depositing the oxynitride film on the substrate by a CVD process, while simultaneously processing the oxynitride film thus deposited by atomic state oxygen and hydrogen nitride radicals formed in plasma.
The inventions also provide a method of forming an oxynitride film, characterized by the steps of:
forming plasma in a processing chamber by introducing an inert gas of Kr or Ar, an oxygen gas, and a gas containing nitrogen and hydrogen into said processing chamber and causing microwave excitation therein;
depositing an oxynitride film on a substrate by introducing a processing gas into said processing chamber and by causing activation of said processing gas by said plasma,
said oxynitride film being processed by atomic state oxygen and hydrogen nitride radicals formed in said plasma simultaneously to deposition.
The inventions also provide a method of forming an oxide film on a substrate by depositing the oxide film on the substrate by a sputtering process, while simultaneously processing the oxide film thus deposited by atomic state oxygen formed in plasma.
The inventions also provide a method of sputtering an oxide film, including:
depositing an oxide film on a substrate in a processing chamber by a sputtering of a target;
forming plasma in said processing chamber by causing microwave excitation of an inert gas of Kr or Ar and an oxygen gas; and
processing said oxide film by atomic state oxygen O* formed in said plasma.
The inventions also provide a method of forming a nitride film on a substrate by depositing the nitride film by a sputtering process, while simultaneously processing the deposited nitride film by hydrogen nitride radicals formed in plasma.
The inventions also provide a sputtering method of an oxide film, characterized by the steps of:
depositing a nitride film on a substrate in a processing chamber by a sputtering of a target;
forming plasma in said processing chamber by microwave excitation of an inert gas of Kr or Ar and a gas containing nitrogen and hydrogen; and
processing said nitride film by hydrogen nitride radicals formed in said plasma.
The inventions also provide a method of forming an oxynitride film on a substrate by depositing the oxynitride film on the substrate by a sputtering process, while simultaneously processing the oxynitride film thus deposited by atomic state oxygen and hydrogen nitride radicals formed in plasma.
The inventions also provide a sputtering method of an oxynitride film, including:
depositing an oxynitride film on a substrate by a sputtering of a target;
forming plasma in said processing chamber by microwave excitation of an inert gas of Kr or Ar, an oxygen gas, and a gas containing nitrogen and hydrogen; and
processing said oxynitride film by atomic state oxygen O* and hydrogen nitride radicals NH* formed in said plasma.
The inventions also provide a gate insulation film on a substrate by stacking a nitride film and a high dielectric film.
The inventions also provide a method of forming a gate insulation film on a substrate, including:
forming a nitride film on a surface of a substrate;
processing said nitride film by hydrogen nitride radicals NH*;
depositing a high dielectric film on said processed nitride film; and
forming a nitride film by processing a surface of said high dielectric film by hydrogen nitride radicals NH*.
The inventions also provide a method of forming a gate insulation film on a substrate, including:
forming an oxynitride film on a substrate;
processing said oxynitride film by hydrogen nitride radicals NH* and atomic state oxygen O*;
depositing a high dielectric film on said processed oxynitride film; and
forming a nitride film by processing a surface of said high dielectric film by hydrogen nitride radicals NH*.